Exhaust gas clean up process
First Claim
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1. A method of regenerating a spent absorbent used in removing NOx and SO2 from exhaust gases, said absorbent including sulfite and bisulfite ions and a metal chelate at least partially loaded with NOx values, said method comprising:
- heating and venting the loaded absorbent for at least 4 hours at a temperature of at least 60°
C. to regenerate the metal chelate in respect to NOx absorption;
depleting sulfite and bisulfite ions from said absorbent in a first compartment of an electrodialysis cell having an anode and cathode, said first compartment defined between a first cation selective membrane disposed towards the cathode and an anion selective membrane disposed toward the anode;
concentrating sulfite and bisulfite ions in an aqueous solution in a second compartment adjacent to said first compartment across said anion selective membrane in the electrodialysis cell, said second compartment defined between said anion selective membrane and a second cation selective membrane towards said anode;
oxidizing a portion of the sulfite concentrated in the second compartment to form a sulfate salt and drying the sulfate salt to a solid for withdrawal;
adding a soluble carbonate to the spent absorbent to convert bisulfite to sulfite ions and thereby regenerate the absorbent in respect to SO2 absorption;
returning the regenerated absorbent into contact with said exhaust gases.
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Abstract
A method of cleaning an exhaust gas containing particulates, SO2 and NOx includes prescrubbing with water to remove HCl and most of the particulates, scrubbing with an aqueous absorbent containing a metal chelate and dissolved sulfite salt to remove NOx and SO2, and regenerating the absorbent solution by controlled heating, electrodialysis and carbonate salt addition. The NOx is removed as N2 or nitrogen-sulfonate ions and the oxides of sulfur are removed as a vaulable sulfate salt.
21 Citations
19 Claims
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1. A method of regenerating a spent absorbent used in removing NOx and SO2 from exhaust gases, said absorbent including sulfite and bisulfite ions and a metal chelate at least partially loaded with NOx values, said method comprising:
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heating and venting the loaded absorbent for at least 4 hours at a temperature of at least 60°
C. to regenerate the metal chelate in respect to NOx absorption;depleting sulfite and bisulfite ions from said absorbent in a first compartment of an electrodialysis cell having an anode and cathode, said first compartment defined between a first cation selective membrane disposed towards the cathode and an anion selective membrane disposed toward the anode; concentrating sulfite and bisulfite ions in an aqueous solution in a second compartment adjacent to said first compartment across said anion selective membrane in the electrodialysis cell, said second compartment defined between said anion selective membrane and a second cation selective membrane towards said anode; oxidizing a portion of the sulfite concentrated in the second compartment to form a sulfate salt and drying the sulfate salt to a solid for withdrawal; adding a soluble carbonate to the spent absorbent to convert bisulfite to sulfite ions and thereby regenerate the absorbent in respect to SO2 absorption; returning the regenerated absorbent into contact with said exhaust gases. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of cleaning an exhaust gas containing SOx and NOx comprising:
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scrubbing said exhaust gas with an aqueous absorbent containing a sulfite and a metal chelate, said sulfite acting to take up SO2 and water to form bisulfite and said metal chelate acting to take up NOx as the absorbent is loaded, heating the loaded absorbent to at least 60°
C. for at least 4 hours to regenerate the metal chelate,passing the aqueous absorbent through a first compartment from which ions are depleted in an electrodialysis stack having a cathode and an anode, said first compartment defined between a cation selective membrane disposed towards the cathode and an anion selective membrane disposed toward the anode, passing an aqueous solution through a second compartment into which ions are concentrated in said electrodialysis stack adjacent to said first compartment across said anion selective membrane, said second compartment defined between said anion selective membrane and a second cation selective membrane towards said anode, passing an electrical current between said anode and cathode to transfer sulfite and bisulfite from the first compartment into the second compartment, adding carbonate to said absorbent to convert bisulfite to sulfite and returning the aqueous absorbent into scrubbing contact with said exhaust gases. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19)
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Specification